In recent years, since the punch-through resistance has been strengthened to enable formation of short-channel transistors, semiconductor devices having a double-gate structure or a triple-gate structure have been proposed. The structure is such that a concave-convex portion is formed on a silicon substrate surface, a gate insulating film and a gate electrode are formed on side surfaces and an upper surface of the concave-convex portion, and the side surfaces or the side surfaces and upper surface of the silicon substrate surface are used as channels of a transistor. When the two side surfaces are used as the channels, it is called the double-gate structure, while, when the two side surfaces and the upper surface are used as the channels, it is called the triple-gate structure.
Not only in the case of the double-gate structure or the triple-gate structure, but also in the case of a single-gate structure, a gate insulating film such as a silicon oxide film is formed on the substrate surface. Conventionally, a silicon oxide film has been formed as a gate insulating film by a thermal oxidation technique.
However, when the gate insulating film is formed on the substrate surface by thermal treatment in the semiconductor device of the double-gate structure or the triple-gate structure, the interface states between silicon and the insulating film (Si/SiO2) increase other than in a (100) crystal orientation to degrade the quality of the oxide film and, therefore, it has been difficult to obtain good characteristics as the semiconductor device. Further, there is a problem that the insulating film cannot be formed uniform at edge portions of the three-dimensional structure, and so on, so that an excellent gate insulating film cannot be obtained.
This invention has been made under the circumstances as described above and has an object to provide a semiconductor device manufacturing method that contributes to an improvement in characteristics of a semiconductor device, and a semiconductor device manufactured by such a manufacturing method.